refactor: reorganize message handling for better type safety and clarity (#239)

* refactor: improve typing with memory stream type aliases

Move memory stream type definitions to models.py and use them throughout
the codebase for better type safety and maintainability.

GitHub-Issue:#201

* refactor: move streams to ParsedMessage

* refactor: update test files to use ParsedMessage

Updates test files to work with the ParsedMessage stream type aliases
and fixes a line length issue in test_201_client_hangs_on_logging.py.

Github-Issue:#201

* refactor: rename ParsedMessage to MessageFrame for clarity

🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>

* refactor: move MessageFrame class to types.py for better code organization

🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>

* fix pyright

* refactor: update websocket client to use MessageFrame

Modified the websocket client to work with the new MessageFrame type,
preserving raw message text and properly extracting the root JSON-RPC
message when sending.

Github-Issue:#204

* fix: use NoneType instead of None for type parameters in MessageFrame

🤖 Generated with [Claude Code](https://claude.ai/code)

* refactor: rename root to message

src/mcp/client/session.py

@@ -1,12 +1,11 @@
 from datetime import timedelta
 from typing import Any, Protocol
 
-from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
 from pydantic import AnyUrl, TypeAdapter
 
 import mcp.types as types
 from mcp.shared.context import RequestContext
-from mcp.shared.session import BaseSession, RequestResponder
+from mcp.shared.session import BaseSession, ReadStream, RequestResponder, WriteStream
 from mcp.shared.version import SUPPORTED_PROTOCOL_VERSIONS
 
 
@@ -59,8 +58,8 @@ class ClientSession(
 ):
     def __init__(
         self,
-        read_stream: MemoryObjectReceiveStream[types.JSONRPCMessage | Exception],
-        write_stream: MemoryObjectSendStream[types.JSONRPCMessage],
+        read_stream: ReadStream,
+        write_stream: WriteStream,
         read_timeout_seconds: timedelta | None = None,
         sampling_callback: SamplingFnT | None = None,
         list_roots_callback: ListRootsFnT | None = None,

src/mcp/client/sse.py

@@ -6,10 +6,16 @@ from urllib.parse import urljoin, urlparse
 import anyio
 import httpx
 from anyio.abc import TaskStatus
-from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
 from httpx_sse import aconnect_sse
 
 import mcp.types as types
+from mcp.shared.session import (
+    ReadStream,
+    ReadStreamWriter,
+    WriteStream,
+    WriteStreamReader,
+)
+from mcp.types import MessageFrame
 
 logger = logging.getLogger(__name__)
 
@@ -31,11 +37,11 @@ async def sse_client(
     `sse_read_timeout` determines how long (in seconds) the client will wait for a new
     event before disconnecting. All other HTTP operations are controlled by `timeout`.
     """
-    read_stream: MemoryObjectReceiveStream[types.JSONRPCMessage | Exception]
-    read_stream_writer: MemoryObjectSendStream[types.JSONRPCMessage | Exception]
+    read_stream: ReadStream
+    read_stream_writer: ReadStreamWriter
 
-    write_stream: MemoryObjectSendStream[types.JSONRPCMessage]
-    write_stream_reader: MemoryObjectReceiveStream[types.JSONRPCMessage]
+    write_stream: WriteStream
+    write_stream_reader: WriteStreamReader
 
     read_stream_writer, read_stream = anyio.create_memory_object_stream(0)
     write_stream, write_stream_reader = anyio.create_memory_object_stream(0)
@@ -84,8 +90,11 @@ async def sse_client(
 
                                     case "message":
                                         try:
-                                            message = types.JSONRPCMessage.model_validate_json(  # noqa: E501
-                                                sse.data
+                                            message = MessageFrame(
+                                                message=types.JSONRPCMessage.model_validate_json(  # noqa: E501
+                                                    sse.data
+                                                ),
+                                                raw=sse,
                                             )
                                             logger.debug(
                                                 f"Received server message: {message}"

src/mcp/client/websocket.py

@@ -1,7 +1,7 @@
 import json
 import logging
 from contextlib import asynccontextmanager
-from typing import AsyncGenerator
+from typing import Any, AsyncGenerator
 
 import anyio
 from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
@@ -10,6 +10,7 @@ from websockets.asyncio.client import connect as ws_connect
 from websockets.typing import Subprotocol
 
 import mcp.types as types
+from mcp.types import MessageFrame
 
 logger = logging.getLogger(__name__)
 
@@ -19,8 +20,8 @@ async def websocket_client(
     url: str,
 ) -> AsyncGenerator[
     tuple[
-        MemoryObjectReceiveStream[types.JSONRPCMessage | Exception],
-        MemoryObjectSendStream[types.JSONRPCMessage],
+        MemoryObjectReceiveStream[MessageFrame[Any] | Exception],
+        MemoryObjectSendStream[MessageFrame[Any]],
     ],
     None,
 ]:
@@ -53,7 +54,11 @@ async def websocket_client(
             async with read_stream_writer:
                 async for raw_text in ws:
                     try:
-                        message = types.JSONRPCMessage.model_validate_json(raw_text)
+                        json_message = types.JSONRPCMessage.model_validate_json(
+                            raw_text
+                        )
+                        # Create MessageFrame with JSON message as root
+                        message = MessageFrame(message=json_message, raw=raw_text)
                         await read_stream_writer.send(message)
                     except ValidationError as exc:
                         # If JSON parse or model validation fails, send the exception
@@ -66,8 +71,8 @@ async def websocket_client(
             """
             async with write_stream_reader:
                 async for message in write_stream_reader:
-                    # Convert to a dict, then to JSON
-                    msg_dict = message.model_dump(
+                    # Extract the JSON-RPC message from MessageFrame and convert to JSON
+                    msg_dict = message.message.model_dump(
                         by_alias=True, mode="json", exclude_none=True
                     )
                     await ws.send(json.dumps(msg_dict))